RF Renal Denervation Catheter with Multiple Independent Electrodes

ABSTRACT

A catheter includes a flexible shaft having a length sufficient to access a patient&#39;s renal artery relative to a percutaneous access location. The catheter includes a multiplicity of elongated resilient members each comprising a pre-formed curve and extendable beyond the catheter. The resilient members are constrained to a low profile when encompassed by a removable sheath, and expand outwardly to assume a pre-defined shape when removed from the sheath. An electrode assembly is provided at a distal end of each resilient member, and includes an electrode element coupled to an electrical conductor and a thermal sensor in thermal communication with the electrode element. The resilient members have a stiffness sufficient to maintain contact between the electrode elements and an inner wall of the renal artery including irregularities of the inner wall of the renal artery during ablation of perivascular renal nerve tissue.

RELATED PATENT DOCUMENTS

This application claims the benefit of Provisional Patent Application Ser. No. 61/407,324 filed Oct. 27, 2010, to which priority is claimed pursuant to 35 U.S.C. §119(e) and which are hereby incorporated herein by reference.

SUMMARY

Embodiments of the disclosure are directed to an apparatus which includes a catheter having a flexible shaft and a multiplicity of elongated resilient members each comprising a pre-formed curve and extendable beyond a distal end of the catheter. The resilient members are constrained to a low profile when encompassed by a wall of a removable sheath or a lumen wall of the shaft. When removed from the removable sheath or lumen of the shaft, the resilient members expand outwardly and assume a shape of the pre-formed curve. An electrode assembly is provided at a distal end of each of the resilient members. Each of the electrode assemblies include an electrode element coupled to an electrical conductor and a thermal sensor in thermal communication with the electrode element. The resilient members preferably have a stiffness sufficient to maintain contact between the electrode elements and an inner wall of a target vessel of the body including irregularities of the inner wall of the target vessel.

According to various embodiments, and apparatus includes a catheter having a flexible shaft with a proximal end, a distal end, and a length. The length of the shaft is preferably sufficient to access a patient's renal artery relative to a percutaneous access location. The catheter includes a multiplicity of elongated resilient members each comprising a pre-formed curve and extendable beyond the distal end of the catheter. The resilient members are constrained to a low profile when encompassed by a wall of a removable sheath or a lumen wall of the shaft. When removed from the removable sheath or lumen of the shaft, the resilient members expand outwardly and assume a shape of the pre-formed curve. An electrode assembly is provided at a distal end of each of the resilient members. Each of the electrode assemblies includes an electrode element coupled to an electrical conductor and a thermal sensor in thermal communication with the electrode element. The resilient members preferably have a stiffness sufficient to maintain contact between the electrode elements and an inner wall of the renal artery including irregularities of the inner wall of the renal artery.

In accordance with other embodiments, a method involves constraining a multiplicity of electrode assemblies each supported by one of a multiplicity of elongated support members to a low profile configuration within a removable sheath or a lumen of a catheter shaft. The method also involve moving the electrode assemblies and elongated support members free of the sheath or catheter shaft lumen within a target vessel to allow the electrode assemblies to assume a pre-formed shape and expand outwardly to contact an inner wall of the target vessel. The method further involves resiliently maintaining contact between each electrode assembly and the inner wall of the target vessel including irregularities of the inner wall of the target vessel, and ablating target tissue using the electrode assemblies.

These and other features can be understood in view of the following detailed discussion and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a right kidney and renal vasculature including a renal artery branching laterally from the abdominal aorta;

FIGS. 2A and 2B illustrate sympathetic innervation of the renal artery;

FIG. 3A illustrates various tissue layers of the wall of the renal artery;

FIGS. 3B and 3C illustrate a portion of a renal nerve;

FIG. 4 illustrates an apparatus for ablating target tissue of a vessel of the body in accordance with various embodiments;

FIG. 5 schematically illustrates a cross-section of an electrode assembly mounted at a distal end of a resilient support member in accordance with various embodiments;

FIG. 6 shows a catheter which incorporates a therapy element in a low-profile introduction configuration in accordance with various embodiments;

FIG. 7 shows different configurations of a resilient support member and an electrode assembly in accordance with various embodiments;

FIG. 8 illustrates a treatment element of an ablation catheter which includes a unitary multiple-electrode and resilient support member structure in accordance with various embodiments;

FIGS. 9 and 10 show a swiveling electrical hub for establishing connection with a connector of an external control unit in accordance with various embodiments; and

FIG. 11 shows a representative RF renal therapy apparatus in accordance with various embodiments of the disclosure.

DETAILED DESCRIPTION

Embodiments of the disclosure are directed to apparatuses and methods for ablating extravascular target tissue from within a vessel. Embodiments of the disclosure are directed to apparatuses and methods for ablating perivascular renal nerves from within the renal artery or other nearby vessel for the treatment of hypertension. Apparatuses are directed to an RF catheter with multiple independent electrode arrangements disposed on radially extensible resilient members protruding from a distal tip of an ablation catheter for delivering ablation therapy to target tissue from within a vessel.

Ablation of perivascular renal nerves has been used as a treatment for hypertension. RF electrodes placed in the renal artery can be used to ablate the nerves, but with risk of artery wall injury. To control injury to the artery wall, one approach is to ablate at discrete locations along and around the artery. Maintaining good electrode contact with the artery wall during ablation of perivascular renal nerves has been difficult, often resulting in poor control of tissue temperatures for effective ablation and risk of significant artery damage. In addition, reliable control of electrode position has been difficult. Overcoming catheter or electrode “whip” as it is moved around in the artery, for example, makes desired electrode positioning challenging. Also, multiple repositioning and ablation cycles are considered undesirable and time-consuming.

Embodiments of the disclosure include electrode assemblies provided on pre-formed curved ends of resilient members extending from a distal tip of an ablation catheter. Each of the electrode assemblies include an electrode element, a thermal sensor in thermal communication with the electrode element, and an electrical conductor electrically coupled to the electrode element. According to various embodiments, the resilient members have a stiffness sufficient to maintain contact between the electrode elements and an inner wall of the renal artery including irregularities of the inner wall of the renal artery when the resilient members are removed from a removable sheath for deployment within the renal artery.

Multiple electrodes spaced circumferentially and axially can be used to ablate the perivascular renal nerves while minimizing renal artery injury. Some prior approaches have included use of a temperature sensor on an ablation catheter system, but a single temperature sensor may provide insufficient information to properly control a system with multiple electrodes placed at various circumferential and axial locations. Embodiments of the disclosure advantageously place multiple electrodes in a predictable pattern, in good contact with the artery wall, and with local temperature monitoring for each electrode.

Embodiments of the disclosure are directed to apparatuses and methods for RF ablation of perivascular renal nerves for treatment of hypertension. Various embodiments disclosed herein are directed to apparatuses and methods that utilize multiple electrodes on a single device for reliable positioning at different axial and circumferential locations in the artery, with temperature and/or impedance monitoring for each electrode, in a simple structure. In some embodiments, the distal portion of an ablation device includes multiple electrode assemblies in a desired spacing and pattern for effective ablation of perivascular renal nerves, so that no repositioning of electrodes is required.

Each electrode assembly includes a curved, protruding electrode structure configured to contact the artery wall during use, a power wire to supply RF energy from an external control unit, and a thermocouple or other temperature sensor. Each electrode assembly is a mounted at the distal portion of an elastic metal apposition wire or ribbon.

According to some embodiments, temperature at or near the electrode elements and/or electrode-tissue can be measured using an optical fiber that extends along the catheter shaft, along the apposition wire, and terminates at or near the electrode assembly. In some configurations, temperature measurements can made by an optical fiber that has evanescent loss that varies with temperature, or by analyzing the Raman scattering of the optical fiber. In some embodiments, the electrical voltage or electric field during ablation can be sensed by nonlinear optical effects in specially-doped optical fiber, which alter the polarization of light as a function of voltage or electric field.

According to some embodiments, impedance can be measured and monitored for each electrode assembly, in a unipolar configuration, or between electrode assemblies, in a bipolar configuration. Changes in tissue impedance due to heating and ablation can be monitored by an external control unit, alone or along with temperature monitoring, to enable automatic or semi-automatic control of an ablation procedure.

The apposition wires may be constructed of superelastic nickel titanium alloy, stainless steel, or other spring-like or self-expanding type materials, and are formed so that they are biased outward to force the electrode assemblies against the artery wall. An external sheath can be used to constrain the electrodes for introduction and delivery of the ablation device. The apposition wires are preferably pre-curved with a relaxed configuration that self-deploys to press the electrode against the artery wall. A variety of curved and bent shapes can be utilized. A wide variety of useful electrode shapes are contemplated.

In other embodiments, a similar multiple-electrode structure is provided. Rather than using multiple separate elastic wires, a single metallic tube is cut to form multiple longitudinal strips or ribbons, with the electrodes mounted at the distal ends of the strips. For example, a Nitinol hypo tube can have strips formed at the distal end by laser cutting or other fabrication method, so that the ends of the strips are at different axial and circumferential locations. An electrode assembly is provided at the distal end of each strip, with a power wire, a thermocouple, and a protruding electrode structure. An external sheath is provided to constrain the device in a low-profile configuration for introduction and advancement within the vasculature.

An external control unit can be coupled to the ablation catheter to provide RF energy and temperature monitoring. A swiveling electrical connector or hub can be provided at the proximal end of the ablation catheter, to allow the catheter hub to rotate. The swiveling electrical connector at the hub end of the ablation catheter is configured to couple to a cable or connector of an external control unit. The swiveling electrical connector provides for rotation of the catheter while being navigated within the vasculature. The swiveling electrical connector can utilize multiple sliding electrical contacts for unlimited rotation, or a multifilament wire structure which allows limited catheter rotation by winding up or unwinding the multifilament structure.

Various embodiments of the disclosure are directed to apparatuses and methods for renal denervation for treating hypertension. Hypertension is a chronic medical condition in which the blood pressure is elevated. Persistent hypertension is a significant risk factor associated with a variety of adverse medical conditions, including heart attacks, heart failure, arterial aneurysms, and strokes. Persistent hypertension is a leading cause of chronic renal failure. Hyperactivity of the sympathetic nervous system serving the kidneys is associated with hypertension and its progression. Deactivation of nerves in the kidneys via renal denervation can reduce blood pressure, and may be a viable treatment option for many patients with hypertension who do not respond to conventional drugs.

The kidneys are instrumental in a number of body processes, including blood filtration, regulation of fluid balance, blood pressure control, electrolyte balance, and hormone production. One primary function of the kidneys is to remove toxins, mineral salts, and water from the blood to form urine. The kidneys receive about 20-25% of cardiac output through the renal arteries that branch left and right from the abdominal aorta, entering each kidney at the concave surface of the kidneys, the renal hilum.

Blood flows into the kidneys through the renal artery and the afferent arteriole, entering the filtration portion of the kidney, the renal corpuscle. The renal corpuscle is composed of the glomerulus, a thicket of capillaries, surrounded by a fluid-filled, cup-like sac called Bowman's capsule. Solutes in the blood are filtered through the very thin capillary walls of the glomerulus due to the pressure gradient that exists between the blood in the capillaries and the fluid in the Bowman's capsule. The pressure gradient is controlled by the contraction or dilation of the arterioles. After filtration occurs, the filtered blood moves through the efferent arteriole and the peritubular capillaries, converging in the interlobular veins, and finally exiting the kidney through the renal vein.

Particles and fluid filtered from the blood move from the Bowman's capsule through a number of tubules to a collecting duct. Urine is formed in the collecting duct and then exits through the ureter and bladder. The tubules are surrounded by the peritubular capillaries (containing the filtered blood). As the filtrate moves through the tubules and toward the collecting duct, nutrients, water, and electrolytes, such as sodium and chloride, are reabsorbed into the blood.

The kidneys are innervated by the renal plexus which emanates primarily from the aorticorenal ganglion. Renal ganglia are formed by the nerves of the renal plexus as the nerves follow along the course of the renal artery and into the kidney. The renal nerves are part of the autonomic nervous system which includes sympathetic and parasympathetic components. The sympathetic nervous system is known to be the system that provides the bodies “fight or flight” response, whereas the parasympathetic nervous system provides the “rest and digest” response. Stimulation of sympathetic nerve activity triggers the sympathetic response which causes the kidneys to increase production of hormones that increase vasoconstriction and fluid retention. This process is referred to as the renin-angiotensin-aldosterone-system (RAAS) response to increased renal sympathetic nerve activity.

In response to a reduction in blood volume, the kidneys secrete renin, which stimulates the production of angiotensin. Angiotensin causes blood vessels to constrict, resulting in increased blood pressure, and also stimulates the secretion of the hormone aldosterone from the adrenal cortex. Aldosterone causes the tubules of the kidneys to increase the reabsorption of sodium and water, which increases the volume of fluid in the body and blood pressure.

Congestive heart failure (CHF) is a condition that has been linked to kidney function. CHF occurs when the heart is unable to pump blood effectively throughout the body. When blood flow drops, renal function degrades because of insufficient perfusion of the blood within the renal corpuscles. The decreased blood flow to the kidneys triggers an increase in sympathetic nervous system activity (i.e., the RAAS becomes too active) that causes the kidneys to secrete hormones that increase fluid retention and vasorestriction. Fluid retention and vasorestriction in turn increases the peripheral resistance of the circulatory system, placing an even greater load on the heart, which diminishes blood flow further. If the deterioration in cardiac and renal functioning continues, eventually the body becomes overwhelmed, and an episode of heart failure decompensation occurs, often leading to hospitalization of the patient.

FIG. 1 is an illustration of a right kidney 10 and renal vasculature including a renal artery 12 branching laterally from the abdominal aorta 20. In FIG. 1, only the right kidney 10 is shown for purposes of simplicity of explanation, but reference will be made herein to both right and left kidneys and associated renal vasculature and nervous system structures, all of which are contemplated within the context of embodiments of the disclosure. The renal artery 12 is purposefully shown to be disproportionately larger than the right kidney 10 and abdominal aorta 20 in order to facilitate discussion of various features and embodiments of the present disclosure.

The right and left kidneys are supplied with blood from the right and left renal arteries that branch from respective right and left lateral surfaces of the abdominal aorta 20. Each of the right and left renal arteries is directed across the crus of the diaphragm, so as to form nearly a right angle with the abdominal aorta 20. The right and left renal arteries extend generally from the abdominal aorta 20 to respective renal sinuses proximate the hilum 17 of the kidneys, and branch into segmental arteries and then interlobular arteries within the kidney 10. The interlobular arteries radiate outward, penetrating the renal capsule and extending through the renal columns between the renal pyramids. Typically, the kidneys receive about 20% of total cardiac output which, for normal persons, represents about 1200 mL of blood flow through the kidneys per minute.

The primary function of the kidneys is to maintain water and electrolyte balance for the body by controlling the production and concentration of urine. In producing urine, the kidneys excrete wastes such as urea and ammonium. The kidneys also control reabsorption of glucose and amino acids, and are important in the production of hormones including vitamin D, renin and erythropoietin.

An important secondary function of the kidneys is to control metabolic homeostasis of the body. Controlling hemostatic functions include regulating electrolytes, acid-base balance, and blood pressure. For example, the kidneys are responsible for regulating blood volume and pressure by adjusting volume of water lost in the urine and releasing erythropoietin and renin, for example. The kidneys also regulate plasma ion concentrations (e.g., sodium, potassium, chloride ions, and calcium ion levels) by controlling the quantities lost in the urine and the synthesis of calcitrol. Other hemostatic functions controlled by the kidneys include stabilizing blood pH by controlling loss of hydrogen and bicarbonate ions in the urine, conserving valuable nutrients by preventing their excretion, and assisting the liver with detoxification.

Also shown in FIG. 1 is the right suprarenal gland 11, commonly referred to as the right adrenal gland. The suprarenal gland 11 is a star-shaped endocrine gland that rests on top of the kidney 10. The primary function of the suprarenal glands (left and right) is to regulate the stress response of the body through the synthesis of corticosteroids and catecholamines, including cortisol and adrenaline (epinephrine), respectively. Encompassing the kidneys 10, suprarenal glands 11, renal vessels 12, and adjacent perirenal fat is the renal fascia, e.g., Gerota's fascia, (not shown), which is a fascial pouch derived from extraperitoneal connective tissue.

The autonomic nervous system of the body controls involuntary actions of the smooth muscles in blood vessels, the digestive system, heart, and glands. The autonomic nervous system is divided into the sympathetic nervous system and the parasympathetic nervous system. In general terms, the parasympathetic nervous system prepares the body for rest by lowering heart rate, lowering blood pressure, and stimulating digestion. The sympathetic nervous system effectuates the body's fight-or-flight response by increasing heart rate, increasing blood pressure, and increasing metabolism.

In the autonomic nervous system, fibers originating from the central nervous system and extending to the various ganglia are referred to as preganglionic fibers, while those extending from the ganglia to the effector organ are referred to as postganglionic fibers. Activation of the sympathetic nervous system is effected through the release of adrenaline (epinephrine) and to a lesser extent norepinephrine from the suprarenal glands 11. This release of adrenaline is triggered by the neurotransmitter acetylcholine released from preganglionic sympathetic nerves.

The kidneys and ureters (not shown) are innervated by the renal nerves 14. FIGS. 1 and 2A-2B illustrate sympathetic innervation of the renal vasculature, primarily innervation of the renal artery 12. The primary functions of sympathetic innervation of the renal vasculature include regulation of renal blood flow and pressure, stimulation of renin release, and direct stimulation of water and sodium ion reabsorption.

Most of the nerves innervating the renal vasculature are sympathetic postganglionic fibers arising from the superior mesenteric ganglion 26. The renal nerves 14 extend generally axially along the renal arteries 12, enter the kidneys 10 at the hilum 17, follow the branches of the renal arteries 12 within the kidney 10, and extend to individual nephrons. Other renal ganglia, such as the renal ganglia 24, superior mesenteric ganglion 26, the left and right aorticorenal ganglia 22, and celiac ganglia 28 also innervate the renal vasculature. The celiac ganglion 28 is joined by the greater thoracic splanchnic nerve (greater TSN). The aorticorenal ganglia 26 is joined by the lesser thoracic splanchnic nerve (lesser TSN) and innervates the greater part of the renal plexus.

Sympathetic signals to the kidney 10 are communicated via innervated renal vasculature that originates primarily at spinal segments T10-T12 and L1. Parasympathetic signals originate primarily at spinal segments S2-S4 and from the medulla oblongata of the lower brain. Sympathetic nerve traffic travels through the sympathetic trunk ganglia, where some may synapse, while others synapse at the aorticorenal ganglion 22 (via the lesser thoracic splanchnic nerve, i.e., lesser TSN) and the renal ganglion 24 (via the least thoracic splanchnic nerve, i.e., least TSN). The postsynaptic sympathetic signals then travel along nerves 14 of the renal artery 12 to the kidney 10. Presynaptic parasympathetic signals travel to sites near the kidney 10 before they synapse on or near the kidney 10.

With particular reference to FIG. 2A, the renal artery 12, as with most arteries and arterioles, is lined with smooth muscle 34 that controls the diameter of the renal artery lumen 13. Smooth muscle, in general, is an involuntary non-striated muscle found within the media layer of large and small arteries and veins, as well as various organs. The glomeruli of the kidneys, for example, contain a smooth muscle-like cell called the mesangial cell. Smooth muscle is fundamentally different from skeletal muscle and cardiac muscle in terms of structure, function, excitation-contraction coupling, and mechanism of contraction.

Smooth muscle cells can be stimulated to contract or relax by the autonomic nervous system, but can also react on stimuli from neighboring cells and in response to hormones and blood borne electrolytes and agents (e.g., vasodilators or vasoconstrictors). Specialized smooth muscle cells within the afferent arteriole of the juxtaglomerular apparatus of kidney 10, for example, produces renin which activates the angiotension II system.

The renal nerves 14 innervate the smooth muscle 34 of the renal artery wall 15 and extend lengthwise in a generally axial or longitudinal manner along the renal artery wall 15. The smooth muscle 34 surrounds the renal artery circumferentially, and extends lengthwise in a direction generally transverse to the longitudinal orientation of the renal nerves 14, as is depicted in FIG. 2B.

The smooth muscle 34 of the renal artery 12 is under involuntary control of the autonomic nervous system. An increase in sympathetic activity, for example, tends to contract the smooth muscle 34, which reduces the diameter of the renal artery lumen 13 and decreases blood perfusion. A decrease in sympathetic activity tends to cause the smooth muscle 34 to relax, resulting in vessel dilation and an increase in the renal artery lumen diameter and blood perfusion. Conversely, increased parasympathetic activity tends to relax the smooth muscle 34, while decreased parasympathetic activity tends to cause smooth muscle contraction.

FIG. 3A shows a segment of a longitudinal cross-section through a renal artery, and illustrates various tissue layers of the wall 15 of the renal artery 12. The innermost layer of the renal artery 12 is the endothelium 30, which is the innermost layer of the intima 32 and is supported by an internal elastic membrane. The endothelium 30 is a single layer of cells that contacts the blood flowing though the vessel lumen 13. Endothelium cells are typically polygonal, oval, or fusiform, and have very distinct round or oval nuclei. Cells of the endothelium 30 are involved in several vascular functions, including control of blood pressure by way of vasoconstriction and vasodilation, blood clotting, and acting as a barrier layer between contents within the lumen 13 and surrounding tissue, such as the membrane of the intima 32 separating the intima 32 from the media 34, and the adventitia 36. The membrane or maceration of the intima 32 is a fine, transparent, colorless structure which is highly elastic, and commonly has a longitudinal corrugated pattern.

Adjacent the intima 32 is the media 33, which is the middle layer of the renal artery 12. The media is made up of smooth muscle 34 and elastic tissue. The media 33 can be readily identified by its color and by the transverse arrangement of its fibers. More particularly, the media 33 consists principally of bundles of smooth muscle fibers 34 arranged in a thin plate-like manner or lamellae and disposed circularly around the arterial wall 15. The outermost layer of the renal artery wall 15 is the adventitia 36, which is made up of connective tissue. The adventitia 36 includes fibroblast cells 38 that play an important role in wound healing.

A perivascular region 37 is shown adjacent and peripheral to the adventitia 36 of the renal artery wall 15. A renal nerve 14 is shown proximate the adventitia 36 and passing through a portion of the perivascular region 37. The renal nerve 14 is shown extending substantially longitudinally along the outer wall 15 of the renal artery 12. The main trunk of the renal nerves 14 generally lies in or on the adventitia 36 of the renal artery 12, often passing through the perivascular region 37, with certain branches coursing into the media 33 to enervate the renal artery smooth muscle 34.

Embodiments of the disclosure may be implemented to provide varying degrees of denervation therapy to innervated renal vasculature. For example, embodiments of the disclosure may provide for control of the extent and relative permanency of renal nerve impulse transmission interruption achieved by denervation therapy delivered using a treatment apparatus of the disclosure. The extent and relative permanency of renal nerve injury may be tailored to achieve a desired reduction in sympathetic nerve activity (including a partial or complete block) and to achieve a desired degree of permanency (including temporary or irreversible injury).

Returning to FIGS. 3B and 3C, the portion of the renal nerve 14 shown in FIGS. 3B and 3C includes bundles 14 a of nerve fibers 14 b each comprising axons or dendrites that originate or terminate on cell bodies or neurons located in ganglia or on the spinal cord, or in the brain. Supporting tissue structures 14 c of the nerve 14 include the endoneurium (surrounding nerve axon fibers), perineurium (surrounds fiber groups to form a fascicle), and epineurium (binds fascicles into nerves), which serve to separate and support nerve fibers 14 b and bundles 14 a. In particular, the endoneurium, also referred to as the endoneurium tube or tubule, is a layer of delicate connective tissue that encloses the myelin sheath of a nerve fiber 14 b within a fasciculus.

Major components of a neuron include the soma, which is the central part of the neuron that includes the nucleus, cellular extensions called dendrites, and axons, which are cable-like projections that carry nerve signals. The axon terminal contains synapses, which are specialized structures where neurotransmitter chemicals are released in order to communicate with target tissues. The axons of many neurons of the peripheral nervous system are sheathed in myelin, which is formed by a type of glial cell known as Schwann cells. The myelinating Schwann cells are wrapped around the axon, leaving the axolemma relatively uncovered at regularly spaced nodes, called nodes of Ranvier. Myelination of axons enables an especially rapid mode of electrical impulse propagation called saltation.

In some embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes transient and reversible injury to renal nerve fibers 14 b. In other embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes more severe injury to renal nerve fibers 14 b, which may be reversible if the therapy is terminated in a timely manner. In preferred embodiments, a treatment apparatus of the disclosure may be implemented to deliver denervation therapy that causes severe and irreversible injury to renal nerve fibers 14 b, resulting in permanent cessation of renal sympathetic nerve activity. For example, a treatment apparatus may be implemented to deliver a denervation therapy that disrupts nerve fiber morphology to a degree sufficient to physically separate the endoneurium tube of the nerve fiber 14 b, which can prevent regeneration and re-innervation processes.

By way of example, and in accordance with Seddon's classification as is known in the art, a treatment apparatus of the disclosure may be implemented to deliver a denervation therapy that interrupts conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers 14 b consistent with neruapraxia. Neurapraxia describes nerve damage in which there is no disruption of the nerve fiber 14 b or its sheath. In this case, there is an interruption in conduction of the nerve impulse down the nerve fiber, with recovery taking place within hours to months without true regeneration, as Wallerian degeneration does not occur. Wallerian degeneration refers to a process in which the part of the axon separated from the neuron's cell nucleus degenerates. This process is also known as anterograde degeneration. Neurapraxia is the mildest form of nerve injury that may be imparted to renal nerve fibers 14 b by use of a treatment apparatus according to embodiments of the disclosure.

A treatment apparatus may be implemented to interrupt conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers consistent with axonotmesis. Axonotmesis involves loss of the relative continuity of the axon of a nerve fiber and its covering of myelin, but preservation of the connective tissue framework of the nerve fiber. In this case, the encapsulating support tissue 14 c of the nerve fiber 14 b is preserved. Because axonal continuity is lost, Wallerian degeneration occurs. Recovery from axonotmesis occurs only through regeneration of the axons, a process requiring time on the order of several weeks or months. Electrically, the nerve fiber 14 b shows rapid and complete degeneration. Regeneration and re-innervation may occur as long as the endoneural tubes are intact.

A treatment apparatus may be implemented to interrupt conduction of nerve impulses along the renal nerve fibers 14 b by imparting damage to the renal nerve fibers 14 b consistent with neurotmesis. Neurotmesis, according to Seddon's classification, is the most serious nerve injury in the scheme. In this type of injury, both the nerve fiber 14 b and the nerve sheath are disrupted. While partial recovery may occur, complete recovery is not possible. Neurotmesis involves loss of continuity of the axon and the encapsulating connective tissue 14 c, resulting in a complete loss of autonomic function, in the case of renal nerve fibers 14 b. If the nerve fiber 14 b has been completely divided, axonal regeneration causes a neuroma to form in the proximal stump.

A more stratified classification of neurotmesis nerve damage may be found by reference to the Sunderland System as is known in the art. The Sunderland System defines five degrees of nerve damage, the first two of which correspond closely with neurapraxia and axonotmesis of Seddon's classification. The latter three Sunderland System classifications describe different levels of neurotmesis nerve damage.

The first and second degrees of nerve injury in the Sunderland system are analogous to Seddon's neurapraxia and axonotmesis, respectively. Third degree nerve injury, according to the Sunderland System, involves disruption of the endoneurium, with the epineurium and perineurium remaining intact. Recovery may range from poor to complete depending on the degree of intrafascicular fibrosis. A fourth degree nerve injury involves interruption of all neural and supporting elements, with the epineurium remaining intact. The nerve is usually enlarged. Fifth degree nerve injury involves complete transection of the nerve fiber 14 b with loss of continuity.

Turning now to FIG. 4, there is illustrated an apparatus for ablating target tissue of a vessel of the body in accordance with various embodiments. According to some embodiments, and as shown in FIG. 4, a catheter 100 includes a flexible shaft 104 having a proximal end, a distal end, and a length. The length of the shaft is sufficient to access a target vessel of the body, such as a patient's renal artery 12, relative to a percutaneous access location.

The catheter shaft 104 typically includes a number of lumens, one of which is dimensioned to receive a treatment element 101. The treatment element 101 includes a multiplicity of resilient support members 131 and an electrode assembly 120 supported by a respective support member 131. Each of the support members 131 defines an apposition member or wire that preferably incorporates a pre-formed curve. In some embodiments, the treatment element 101 is fixedly disposed within the lumen of the shaft 104 and is delivered to a target vessel using a flexible sheath. In other embodiments, the treatment element 101 is displaceably disposed within the lumen of the shaft 104, and can be retracted within and extended beyond the distal end of the catheter shaft 104. In further embodiments, individual or pairs of the support members 131 is/are displaceable within a respective lumen of the shaft 104. The catheter 100 can be configured as a guiding catheter or may be delivered to a target vessel using a guiding catheter and/or a flexible delivery sheath. The resilient support members 131 can be constrained to a low profile when encompassed by a wall of a removable sheath or a lumen wall of the shaft 104 and, when removed from the removable sheath or lumen of the shaft 104, the resilient support members 131 expand outwardly and assume a shape of the pre-formed curve.

In FIG. 4, four electrodes 120 are shown for purposes of explanation. It is understood that fewer or greater than four electrodes may be provided in various embodiments, and each electrode can be configured to treat a predefined arc of a target vessel (e.g., 30°, 45°, 60°). For example, between three and six electrodes 120 and corresponding support members 131 may be provided so that at least one full revolution of a target vessel's wall can be treated without having to reposition the catheter shaft 104 to complete the ablation procedure.

As discussed above, the resilient support members 131 are constructed to be collapsible when encompassed by a wall of a removable sheath or lumen wall of the shaft 104, and expand outwardly when removed from the removable sheath or extended from the shaft lumen. The resilient support members 131 are preferably constructed as a single or a multiple element structure, providing high or superelastic properties and good electrical conduction properties. For example, the resilient support members 131 can be constructed to have a shape memory, such that the resilient support members 131 expand outwardly and assume a shape of the pre-formed curve when in a deployed configuration. The resilient support members 131 may be constructed as apposition wires fabricated from superelastic nickel titanium alloy, stainless steel, or other spring-like or self-expanding type materials, and are formed so that they are biased outward to force the electrodes 120 against the wall of a target vessel, such as the renal artery 12. The resilient support members 131 can include both a structural spring-like element (such as elastic or superelastic nitinol or a spring-like stainless steel) and a superior electrical conductor (such as stainless steel or platinum), or a single element can provide both the spring-like support and the electrical conductivity properties.

In some embodiments, the resilient support members 131 are constructed to assume different shapes, such that at least some of the resilient support members 131 expand both longitudinally and circumferentially to assume the shape of their respective pre-formed curves. For example, a distal region of the resilient support members 131, including their respective electrodes 120, can take on a longitudinally spaced configuration when deployed. By way of further example, a distal region of the resilient support members 131, including their respective electrodes 120, can take on a longitudinally spaced and circumferentially offset configuration when deployed. The resilient support members 131 preferably have a stiffness sufficient to maintain contact between the electrodes 120 and an inner wall of the renal artery 12 including irregularities of the renal artery's inner wall.

According to various embodiments, each of the resilient support members 131 is constructed from an electrically conductive material and configured as a wire. Each of the conductive resilient support members 131 is coupled to an electrical conductor disposed in a lumen of the catheter shaft 104. The conductive resilient support members 131 preferably include an electrically insulating material or coating, and the electrical conductors coupled to the resilient support members 131 are electrically insulated from one another (e.g., by way of insulating material/coating or separate lumens within the shaft 104). Electrically insulating the respective resilient support members 131 provides for individual activation and deactivation of each electrode 120 in accordance with a predefined energy delivery protocol.

In accordance with various embodiments, each of the resilient support members 131 is either configured as, or coupled to, an individual conductor that extends along the length of the shaft 104 and configured to couple to a control unit 170. The control unit 170 includes an RF generator that can be controlled to deliver different RF therapies according to various predefined energy delivery protocols 172.

In some approaches, the electrode assemblies 120 can be configured to simultaneously deliver electrical current to the renal artery wall in accordance with a predefined energy delivery protocol implemented by the control unit 170. In other approaches, the electrode assemblies 120 can be configured to sequentially deliver electrical current to the renal artery wall in accordance with a predefined energy delivery protocol implemented by the control unit 170. A unipolar energy delivery configuration can be employed by use of an external pad electrode 175. A bipolar energy delivery configuration can be implemented by selectively activating combinations of the electrode assemblies 120. It is noted that multiple electrodes 120 can be situated on an individual resilient support member 131 each of which is coupled to an individual electrical conductor for operation in a bipolar configuration. In some embodiments, as discussed below, the control unit 170 may include a temperature sensor unit 174 that receives signals from a temperature sensor situated at or near the electrodes 120. The RF generator can be automatically controlled based on temperature at the electrode-tissue interface as indicated by the temperature sensor unit 174.

FIG. 5 schematically illustrates a cross-section of an electrode assembly 120 mounted at a distal end of a resilient support member 131 in accordance with various embodiments. According to the embodiment shown in FIG. 5, each electrode assembly has a curved, protruding electrode structure 120′ that defines the energy delivery element of the electrode assembly 120. The curvature of the protruding electrode structure 120′ allows for inclusion of other components of the electrode assembly 120 within a void defined within the electrode structure 120′. The outer surface of the electrode structure 120′ is configured to contact the wall of a target vessel, such as the renal artery, during use. A power wire or other type of electrical conductor 180 is electrically coupled to the electrode structure 120′ at an electrical contact location 180′ within the void of the electrode structure 120′. A temperature sensor 182, such as a thermocouple, is situated within the electrode structure void and in thermal contact with the electrode structure 120′. In some embodiment, the temperature sensor 182 is mounted on the outer surface of the electrode 120 or next to the electrode 120 on resilient support member 131. A proximal section of the electrical conductor 180 and sensor conductor coupled to the temperature sensor 182 may include or be coated with an electrically insulating material.

According to some embodiments, the resilient support member 131, formed of an electrically conductive material, is coupled to a wire or other elongated conductive member that extends from the resilient support members 131 to the proximal end of the catheter shaft 104. The wire or elongated conductive member is preferably covered with an electrically insulating material or coating up to a location where the wire or elongated conductive member couples to the electrode 120.

FIG. 6 shows a catheter 104 which incorporates a therapy element 101 in a low-profile introduction configuration in accordance with various embodiments. FIG. 6 shows an embodiment where the resilient support members 131 are fixedly positioned at the distal end of the catheter shaft 104 and constrained by the lumen wall of a removable delivery sheath 185. According to one delivery approach, a guidewire (not shown) is advanced through a lumen of the catheter shaft 104 and maneuvered into a destination vessel. The delivery sheath 185 can be advanced over the guidewire and into the destination vessel, and the catheter 100 can be advanced through the delivery sheath 185, with the resilient support members 131 being constrained to a low profile while encompassed by the delivery sheath 185.

According to another delivery approach, a guiding catheter and/or a guidewire can be used to access the destination vessel, and an introducer sheath can be advanced over the guiding catheter/guidewire. The guiding catheter/guidewire are removed and the delivery sheath 185 is advanced through the introducer sheath and into the destination vessel. The introducer sheath may be removed or retracted, and the catheter 100 can be advanced through the delivery sheath 185, with the resilient support members 131 being constrained to a low profile while encompassed by the delivery sheath 185. It is noted that the catheter 100 may be pre-loaded within the delivery sheath 185 prior to advancement through the introducer sheath and into the destination vessel.

With the therapy element 101 situated at a desired location within the destination vessel (e.g., right renal artery), the delivery sheath 185 is retracted, allowing the resilient support members 131 to expand outwardly, assume their pre-determined curved shape, and establish spring-biased contact between the electrode assemblies 120 and discrete locations of the destination vessel wall. Ablation of target tissue adjacent the vessel wall may then be performed. After ablating the target tissue, the sheath 185 and/or catheter 100 may be move axially so that the treatment element 101 is retracted into the lumen of the sheath 185. The catheter 100 and sheath 185 may then be advanced to another destination vessel (e.g., left renal artery), if desired, and the therapy element deployment and ablation procedure repeated. The catheter 100 and sheath 185 may be removed from the body after completion of the ablation procedure(s).

In some embodiments, one or more of the resilient support members 131 can be actively deflectable, such as by actuation of an actuation arrangement (e.g., a pull wire or other elongated member) coupled to the one or more resilient support members 131. For example, a distal end of the pull wire can be connected to a resilient support member 131 at a location proximal of the electrode 120. Tensioning of the pull wire causes the distal end of the resilient support member 131 which includes the electrode 120 to bend outwardly, while relaxation of the pull wire allows the distal end of the resilient support member 131 to straighten. In some, embodiments, a resilient support member 131 equipped with a pull wire can be formed from a biocompatible metal that does not have a shape memory or other spring-like or self-expanding action. In other embodiments, a resilient support member 131 equipped with a pull wire can be formed to have a preferred bending action, which causes resilient support member 131 to bend in a desired direction(s) when actuated by the pull wire.

In some embodiments, a multiplicity of pull wires can extend along the length of the catheter shaft 104 and be coupled to respective resilient support members 131, enabling a clinician to control the deflection of individual resilient support members 131. In other embodiments, a single pull wire can extend along the length of the catheter shaft 104, and be coupled to a coupling arrangement situated at the distal end of the catheter shaft 104. One or more of the resilient support members 131 can be coupled to the coupling arrangement via individual pull wires. A tensile force applied to the single pull wire is translated to the coupling arrangement, which causes tensioning of each individual pull wire and corresponding outward bending of the resilient support members 131. Relaxation of the single pull wire is also translated to the coupling arrangement, which causes each individual pull wire to relax with corresponding straightening of the resilient support members 131.

FIG. 7 shows different configurations of a resilient support member 131 in accordance with various embodiments. A variety of curved and bent shapes can be utilized in the construction of the resilient support members 131. FIG. 7 also shows that a wide variety of useful electrode shapes are possible, some examples of which are illustrated in FIG. 7.

In accordance with various embodiments, and with reference to FIG. 8, a treatment element 201 of an ablation catheter 200 is shown which includes a unitary multiple-electrode and resilient support member structure. Rather than using multiple separate elastic wires as in the case of various embodiments discussed hereinabove, a single metallic tube 202 can be cut to form multiple longitudinal strips or ribbons 131, with electrode assemblies 120 mounted at the distal ends of the strips 131. For example, a Nitinol hypo tube 202 can have strips formed at the distal end by laser cutting or other fabrication method, so that the ends of the strips 131 are at different axial and circumferential locations. An electrode assembly 120 is provided at the distal end of each strip 131. Each of the electrode assemblies includes a power wire or other electrical conductor, a temperature sensor (e.g., thermocouple), and a protruding electrode structure of a type previously discussed. An external sheath is preferably used to constrain the device in a low-profile configuration for introduction and advancement within the vasculature.

FIGS. 9 and 10 illustrate a swiveling electrical coupler for coupling a proximal end of an ablation catheter 100/200 to a cable or connector of an external control unit in accordance with various embodiments. The swiveling electrical coupler provides for rotation of the ablation catheter 100/200 as it is guided within the vasculature. FIG. 9 shows a swiveling electrical hub 280 situated at the proximal end 104′ of a catheter shaft 104. Electrical contacts of the electrical hub 280 are configured to matingly engage electrical contacts of the control unit cable or connector 171. Engagement features of the electrical hub 280 and connector 171 are configured to allow for limited or unlimited relative rotation (swiveling) therebetween. This relative rotation provided between the electrical hub 280 and connector 171 enhances the maneuverability of the catheter 100/200 as it is navigated through the vasculature.

FIG. 10 shows additional details of a swiveling electrical hub 280 in accordance with various embodiments. In FIG. 10, the electrical hub 280 includes four sets 281 of sliding electrical contacts 283, 285, and the control unit connector 171 includes four sets 273 of sliding electrical contacts 287, 289. The sliding electrical contacts 283, 285 of the electrical hub 280 are coupled to respective power and temperature sensor conductors 282 and 284 for each of four electrode assemblies of the treatment element provided at the distal end of the catheter 100/200. The sliding electrical contacts 287, 289 of the control unit connector 171 are coupled to respective power and temperature sensor conductors 286 and 288 for each of four control unit channels. The sliding electrical contact arrangement shown in FIGS. 9 and 10 provides for unlimited relative rotation between the control unit connector 171 and catheter 100/200. In other embodiments, a multifilament wire structure can be used, which allows limited catheter rotation by winding up or unwinding the multifilament structure.

In the embodiment illustrated in FIG. 10, the hub 280 includes a central bore 107 dimensioned to allow passage of a guidewire 290 therethrough. In other embodiments, the hub 280 need not include a central bore 107, but may instead include a guidewire port (not shown) located distal of the hub 280 which is dimensioned to allow passage of a guidewire 290 therethrough. In further embodiments, a swivel hub 280 need not be included in configurations where wind up is not a significant concern.

FIG. 11 shows a representative RF renal therapy apparatus 300 in accordance with various embodiments of the disclosure. The apparatus 300 illustrated in FIG. 11 includes external electrode activation circuitry 320 which comprises power control circuitry 322 and timing control circuitry 324. The external electrode activation circuitry 320, which includes an RF generator, is coupled to temperature measuring circuitry 328 and may be coupled to an optional impedance sensor 326. The catheter 100/200 includes a shaft 104 that incorporates a lumen arrangement configured for receiving a variety of components, such as conductors, pharmacological agents, actuator elements, obturators, sensors, or other components as needed or desired.

The RF generator of the external electrode activation circuitry 320 may include an external pad electrode 330 configured to comfortably engage the patient's back or other portion of the body near the kidneys. Radiofrequency energy produced by the RF generator is coupled to the treatment element 101 at the distal end of the catheter 100/200 by a conductor arrangement disposed in the lumen of the catheter's shaft 104.

Renal denervation therapy using the apparatus shown in FIG. 11 is typically performed using the electrode assemblies 120 of the treatment element 101 positioned within the renal artery 12 and the external pad electrode 330 positioned on the patient's back, with the RF generator operating in a unipolar mode. In this implementation, the electrode assemblies 120 are configured for operation in a unipolar configuration. In other implementations, the electrode assemblies 120 can be configured for operation in a bipolar configuration, in which case the external electrode pad 330 is not needed. The radiofrequency energy flows through the electrode assemblies 120 in accordance with a predetermined activation sequence (e.g., sequential or concurrent) and ablates target tissue which includes renal nerves.

In general, when renal artery tissue temperatures rise above about 113° F. (50° C.), protein is permanently damaged (including those of renal nerve fibers). If heated over about 65° C., collagen denatures and tissue shrinks. If heated over about 65° C. and up to 100° C., cell walls break and oil separates from water. Above about 100° C., tissue desiccates.

According to some embodiments, the electrode activation circuitry 320 is configured to control activation and deactivation of the electrode assemblies 120 in accordance with a predetermined energy delivery protocol and in response to signals received from temperature measuring circuitry 328. The electrode activation circuitry 320 controls radiofrequency energy delivered to the electrode assemblies 120 so as to maintain the current densities at a level sufficient to cause heating of the target tissue to at least a temperature of 55° C.

Temperature sensors 123 situated at the treatment element 101 provide for continuous monitoring of renal artery tissue temperatures, and RF generator power is automatically adjusted so that the target temperatures are achieved and maintained. An impedance sensor arrangement 326 may be used to measure and monitor electrical impedance during RF denervation therapy, and the power and timing of the RF generator 320 may be moderated based on the impedance measurements or a combination of impedance and temperature measurements. The size of the ablated area is determined largely by the size, number, and shape of the electrodes of the electrode sets 120 a-120 n at the treatment element 101, the power applied, and the duration of time the energy is applied.

Marker bands 314 can be placed on one or multiple parts of the treatment element 101 to enable visualization during the procedure. Other portions of the catheter 100/200, such as one or more portions of the shaft 104 (e.g., at hinge mechanism 356), may include a marker band 314. The marker bands 314 may be solid or split bands of platinum or other radiopaque metal, for example. This relatively bright image aids the user in determining specific portions of the catheter 100, such as the distal tip of the catheter 100/200, the treatment element 101, and the hinge 356, for example. A braid and/or electrodes of the catheter 100/200, according to some embodiments, can be radiopaque.

In some embodiments, an expandable arrangement, such as a balloon, basket, or mesh structure, can be situated at the distal end of the catheter 100/200. The expandable arrangement is preferably transformable between a low-profile introduction configuration and a deployed configuration. When the distal end of the catheter 100/200 is advanced into a destination vessel, such as a renal artery 12, the expandable arrangement can be activated, such as by pressurizing a balloon or actuating a push/pull member. Deployment of the expandable arrangement vessel serves to center the treatment element 101 within the vessel 12 and provide stabilization for the treatment element 101 during ablation. After completion of the ablation procedure, the expandable structure can be transformed from its deployed configuration to its low-profile introduction configuration, such as by depressurizing a balloon or actuating a push/pull member.

The embodiments shown in the figures have been generally described in the context of intravascular-based ablation of perivascular renal nerves for control of hypertension. It is understood, however, that embodiments of the disclosure have applicability in other contexts, such as energy delivery from within other vessels of the body, including other arteries, veins, and vasculature (e.g., cardiac and urinary vasculature and vessels), and other tissues of the body, including various organs. Various features and functionality of the ablation catheters disclosed in commonly owned co-pending U.S. patent application Ser. No. 13/188,687, filed on Jul. 22, 2011 and incorporated herein by reference, can be incorporated into a treatment catheter in accordance with various embodiments of the disclosure.

It is to be understood that even though numerous characteristics of various embodiments have been set forth in the foregoing description, together with details of the structure and function of various embodiments, this detailed description is illustrative only, and changes may be made in detail, especially in matters of structure and arrangements of parts illustrated by the various embodiments to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed. 

1. An apparatus, comprising: a catheter comprising a flexible shaft having a proximal end, a distal end, and a length, the length of the shaft sufficient to access a patient's renal artery relative to a percutaneous access location; a plurality of elongated resilient members each comprising a pre-formed curve and extendable beyond the distal end of the catheter, the resilient members constrained to a low profile when encompassed by a wall of a removable sheath or a lumen wall of the shaft and, when removed from the removable sheath or lumen of the shaft, expanding outwardly and assuming a shape of the pre-formed curve; and an electrode assembly provided at a distal end of each of the resilient members, each of the electrode assemblies comprising: an electrode element coupled to an electrical conductor; and a thermal sensor in thermal communication with the electrode element; the resilient members having a stiffness sufficient to maintain contact between the electrode elements and an inner wall of the renal artery including irregularities of the inner wall of the renal artery.
 2. The apparatus of claim 1, comprising the removable sheath, the removable sheath having a length sufficient to access the patient's renal artery relative to the percutaneous access location.
 3. The apparatus of claim 1, wherein the catheter shaft comprises a lumen dimensioned to receive a guidewire.
 4. The apparatus of claim 1, wherein: the electrical conductor extends from the electrode element and along the resilient member; and the thermal sensor comprises a conductor that extends from the thermal sensor and along the resilient member.
 5. The apparatus of claim 1, wherein: the electrical conductor extends from the electrode element, along the resilient member, and is electrically coupled to an electrode conductor arrangement of the catheter shaft; and the thermal sensor comprises a conductor that extends from the thermal sensor, along the resilient member, and is coupled to a sensor conductor arrangement of the catheter shaft.
 6. The apparatus of claim 1, wherein: the electrode element comprises an electrically conductive element having a hallowed out interior; a distal end of the electrical conductor extends into the hallowed out interior and is connected to the conductive element therein; and the thermal sensor extends at least partially into the hallowed out interior and is connected to the conductive element therein.
 7. The apparatus of claim 1, comprising a swiveling electrical connector provided at a hub end of the catheter, the swiveling electrical connector configured to facilitate catheter hub rotation relative to a non-rotatable cable of an external control unit.
 8. The apparatus of claim 7, wherein the catheter shaft and the swiveling electrical connector comprise a lumen dimensioned to receive a guidewire.
 9. The apparatus of claim 1, comprising a metallic tube cut to form a plurality of longitudinal strips or ribbons that define individual elongated resilient members, one of the electrode assemblies mounted at the distal end of one of the plurality of longitudinal strips or ribbons.
 10. The apparatus of claim 1, wherein each of the resilient members comprises an electrically conductive wire constructed from a highly elastic or superelastic material.
 11. The apparatus of claim 1, wherein a distal region of each of the resilient members including the respective electrode assemblies take on a longitudinally spaced configuration.
 12. The apparatus of claim 1, wherein a distal region of each of the resilient members including the respective electrode assemblies take on a longitudinally spaced and circumferentially offset configuration.
 13. The apparatus of claim 1, wherein one or more of the resilient members are coupled to an active deflection arrangement, further wherein actuation of the active deflection arrangement causes one or more of the resilient members to expand outwardly and assume the shape of the pre-formed curve.
 14. An apparatus, comprising: a catheter comprising a flexible shaft; a plurality of elongated resilient members each comprising a pre-formed curve and extendable beyond a distal end of the catheter, the resilient members constrained to a low profile when encompassed by a wall of a removable sheath or a lumen wall of the shaft and, when removed from the removable sheath or lumen of the shaft, expanding outwardly and assuming a shape of the pre-formed curve; and an electrode assembly provided at a distal end of each of the resilient members, each of the electrode assemblies comprising: an electrode element coupled to an electrical conductor; and a thermal sensor in thermal communication with the electrode element; the resilient members having a stiffness sufficient to maintain contact between the electrode elements and an inner wall of a target vessel of the body including irregularities of the inner wall of the target vessel.
 15. The apparatus of claim 14, wherein the catheter shaft comprises a lumen dimensioned to receive a guidewire.
 16. The apparatus of claim 14, comprising a swiveling electrical connector provided at a hub end of the catheter, the swiveling electrical connector configured to facilitate catheter hub rotation relative to a non-rotatable cable of an external control unit.
 17. The apparatus of claim 16, wherein the catheter shaft and the swiveling electrical connector comprise a lumen dimensioned to receive a guidewire.
 18. The apparatus of claim 14, comprising a metallic tube cut to form a plurality of longitudinal strips or ribbons that define individual elongated resilient members, one of the electrode assemblies mounted at the distal end of one of the plurality of longitudinal strips or ribbons.
 19. The apparatus of claim 14, wherein one or more of the resilient members are coupled to an active deflection arrangement, further wherein actuation of the active deflection arrangement causes the one or more of the resilient members to expand outwardly and assume the shape of the pre-formed curve.
 20. A method, comprising: constraining a plurality of electrode assemblies each supported by one of a plurality of elongated support members to a low profile configuration within a removable sheath or a lumen of a catheter shaft; moving the electrode assemblies and elongated support members free of the sheath or catheter shaft lumen within a target vessel to allow the electrode assemblies to assume a pre-formed shape and expand outwardly to contact an inner wall of the target vessel; resiliently maintaining contact between each electrode assembly and the inner wall of the target vessel including irregularities of the inner wall of the target vessel; and ablating target tissue using the electrode assemblies.
 21. The method of claim 20, comprising measuring one or both of temperature and impedance at or proximate the electrodes, and moderating target tissue ablation in response to one or both of temperature and impedance measurements.
 22. The method of claim 20, comprising: after completing ablation, constraining the electrode assemblies and elongated support members to the low profile configuration within the removable sheath or the lumen of the catheter shaft; and removing the electrode assemblies and elongated support members from the target vessel while in the low profile configuration.
 23. The method of claim 20, wherein the target vessel comprises a renal artery and the target tissue comprises perivascular renal nerves. 